The present invention relates generally to gas turbine engines, and, more specifically, to cooling of interstage seals.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor and ignited for generating hot combustion gases. The gases flow downstream through turbine stages which extract energy therefrom for powering the compressor and providing output power such as rotating a fan in a turbofan aircraft engine, for example. A high pressure turbine (HPT) powers the compressor, and a low pressure turbine (LPT) powers the fan with corresponding rotor shafts therebetween.
The HPT may include one or more turbine stages, and in a typical configuration two rows of turbine blades cooperate with corresponding turbine nozzles for extracting energy from the hottest combustion gases discharged from the combustor for powering the compressor. The rotor blades extend outwardly from corresponding rotor disks which are interconnected with each other and with the compressor for rotation therewith.
The second stage turbine nozzle disposed between the first and second stages of rotor blades must be suitably sealed from the disks thereof for preventing loss of the combustion gases from the main flowpath through the stator vanes of the nozzles and rotor blades on the disks.
In a typical configuration, an interstage seal is located between the two disks and cooperates with the turbine nozzle for providing a fluid seal therebetween. The interstage seal is in the form of an annular disk having a plurality of seal teeth projecting radially outwardly which cooperate with a honeycomb seal pad supported from an inner band of the nozzle. The seal disk includes forward and aft seal arms or sleeves which abut the cooperating turbine disks for providing an effective seal therebetween.
The interstage seal rotates with the two disks during operation, with the seal teeth cooperating with the stationary seal pad of the nozzle to define labyrinth seals therewith for limiting fluid flow therebetween.
The interstage seal itself and adjoining components of the turbine disk must be suitably cooled during operation due to the heating effect of the combustion gases. Accordingly, air discharged from the compressor is suitably channeled through radial passages in the hollow nozzle vanes and discharged in a forward cavity or plenum defined between the nozzle inner band and the forward seal sleeve. This cooling air cools the components defining the forward plenum and then leaks through the labyrinth seal into an aft cavity or plenum defined between the nozzle inner band and the aft seal sleeve.
As turbine engines are being designed for additional increase in performance and efficiency, cooling air discharged from the compressor has a correspondingly higher temperature which reduces its ability to cool the HPT components including the interstage seal. This cooling air is channeled through the forward interstage plenum past the seal teeth and into the aft interstage plenum picking up heat therealong.
During normal operation of the engine, the radial gap between the seal teeth and the seal pad varies, and as this gap decreases the amount of cooling air leaking therethrough also decreases and in turn decreases the cooling in the aft interstage plenum.
Accordingly, the loss in cooling effectiveness in the aft interstage plenum is compounded by the initially higher temperature of the compressor discharge air, the reduction in flowrate of that air as the seal gap decreases during operation, and the heating of the cooling air itself as it flows past hot turbine components prior to reaching the aft interstage plenum.
Accordingly, it is desired to provide improved interstage seal cooling for solving these problems.
A turbine nozzle includes a seal pad mounted to a seal support from an inner band thereof. The seal pad is provided for cooperating with seal teeth in an interstage seal. A bypass aperture extends through the seal support to bypass cooling air around the seal pad for providing relatively cool air aft of the seal teeth for improving cooling of the interstage seal in this region.